In the related art, an image forming apparatus such as a Multi Function Peripheral (MFP) forms an image on a sheet using a decolorable color material. The decolorable color material may be decolored when heated to a predetermined high temperature.
An image erasing apparatus erases an image formed with the decolorable color material by heating the material to the predetermined high temperature and enables the sheet to be reused. The reuse of sheets may lead to sheet saving, and as a result, to conservation of the environment.
An image erasing apparatus of one type determines whether or not a sheet is reusable by scanning the surfaces of the sheet. Whether or not the sheet is reusable may be determined based on residual images on the sheet subjected to an erasing process, the condition of the sheet (deformation, damage, staining, and the like). In addition, as a sheet quality deteriorates if the sheet is subjected to the erasing process many times, a sheet subjected to the erasing process more than a certain number of times may be determined to be not reusable.
Further, when one surface of a sheet is subjected to the erasing process more frequently relative to the other surface of the sheet, the sheet may not be suitable for reuse. This is because such a sheet is likely to be curled and, as a result, tends to cause a sheet jam or a non-uniform stacking of sheets in the image erasing apparatus or the image forming apparatus.